I have been seriously considering your girl. This for several reasons.
Firstly and understanding that she has not been kept particularly well in the past and that her feather is very bog-burned in the front, she appears to have a lot more feather than most crossbred Gypsies.
Although very slightly less heavy than most well bred Gypsies, she is still very young. I think she will thicken up a lot in the next two years.
In your area, there are more Appaloosa marked Gypsy Cobs, than anywhere else in the world. Hermit stables has been breeding them for generations. I believe they are just over the border in S. Yorkshire. With this in mind, it would not be unusual to find Appy coloured Gypsies in your area. In fact, there are a few from that stud, here in the US.
If she has been pastured with other horses, and especially younger ones, they could have nibbled her tail.
Unless someone actually witnessed the crossbreeding of a Gypsy and Appaloosa, I tend to think, she might be not a cross at all.
Don't forget to check behind her pasterns constantly, for signs of irritation or problems. Watch for her biting at her feet or rubbing them on something. You don't want a simple case of scratches, to turn into something worse.
Anyway, I could be all wet in my thinking here, but just wanted to run it by you.